1. Field of the Invention
This invention is concerned with novel direct blue dyes particularly suitable for application to paper and other cellulosic substrates from aqueous solution.
2. Description of the Prior Art
The preparation of water-soluble blue dyes suitable for application to paper, cotton or leather from 1-amino-8-naphthol-3,6-disulfonic acid and 4,4'-diamino-2,2'-stilbenedisulfonic acid by tetrazotization of the diamine followed by coupling to this naphthol and a 2-amino-monosulphonic acid naphthol is disclosed in U.S. Pat. No. 4,118,182. The salts of these condensation products with cations in aqueous solution containing urea are taught to provide useful dyes solutions. The alkylation (ethylation or methylation) of the amino group of a hydroxy disulfonic acid naphthyl amine followed by coupling with a diamine to form a blue cotton dye is disclosed in British Patent 5407. U.S. Pat. No. 2,211,752 also discloses the preparation of blue to violet dyes from hydroxy sulfonic acid naphthyl amines with the amino group unsubstituted or substituted with alkyl or phenyl coupled to tetrazotized 4,4'-diamino-diaryl-3,3'-disulphonic acids where the diaryl nucleus is biphenyl or sulphone bridged biphenyl. The preparation of blue dyes suitable for writing inks and stable in aqueous alkali from the sodium salt of tetrazotized 4,4'-diaminostilbene-2,2'-disulfonic acid coupled to 1-amino-8-naphthol-2,4 or 4,6-disulfonic acid is disclosed in U.S. Pat. No. 2,489,463. Offenlegungsschrift 2,223,311 is concerned with image dyestuffs which can be made from 1-amino-8-naphthol disulfonic acids in which the amino group may carry alkyl substitution coupled by azo bonds to a variety of urea bond-containing residues.